Reliable authentication, identification and validation of a coin are required in the modern society in order to ensure efficient production and circulation of coins as a cash payment instrument. The main aspects of coin identification are rejection of counterfeited and foreign coins, correct coin validation and sorting in circulation.
Bimetallic coins consisting of a ring part and a core part and containing at least two different metals or alloys are widely used in the world as circulation and commemorative coins. For example, the worldwide known one and two euro coins consist of a ring and a core from CuNi25 and CuZn20Ni5 alloys. The authentication error rate of such bimetallic coins is low in the coin validating or sorting equipment which measures signals which are dependent on the electromagnetic properties of the coin materials. The problem is that counterfeited coins or foreign coins of comparable dimensions and parameters cannot be reliably identified. In order to increase the coin security, i.e. to improve authentication and validation of both simple one-part coins as well as coins consisting of two parts, it was suggested to provide a centre positioned through-hole in the coin. Examples of such coins are 1 and 5 Norwegian krone coins in addition to 5 Denmark krone coin. Another solution proposes characteristic holes which allow identifying a denomination visually, which is disclosed in WO98/51180.
Documents WO96/18173 and DE102009015579 teach to implement an opening in a bimetallic coin or a coin from a metal-polymer composition for insertion of an electronically identifiable component, like an IC chip or RFID transponder. Although such electronic components possess high specific authentication, the manufacturing of such coins is currently very difficult and expensive. Therefore, such IC or RFID coding is acceptable for circulation coins only under certain circumstances, and cannot be applied to authentication of a large amount of coins.